If you haven't yet, be sure to read Using Muriatic Acid to Safely Lower Your Pool's pH before using the acid.

Calcium Hypochlorite is a pool store chemical but has been recently been mixed with copper and other stuff you don't want in your pool. Ben recommended this: In The Swim Cal-Chlor Pool Chlorine Granules 50 lbs. available at Amazon earlier this season to another poster - it's not adulterated.

If you do decide to use Cal-Hypo, DO NOT let it come in contact with other pool chems or flamable liquids - Goes Boom.